The lipids of the myelin of brain are derived from the oligodendroglial cells whose plasma membranes form the myelin sheaths. Earlier work has demonstrated the microsomal origin of myelin-specific lipids, but the usual "microsomal" fraction of the brain is a highly heterogeneous mixture of membranes. The exact sites of biosynthesis of the myelin-specific lipids: cerebrosides, sulfatides, galactosyldiglycerides, and other lipids accumulating in myelin: polyphosphoinositides, plasmalogens, are not known. It may be presumed that the Golgi apparatus of the glial cells is an important station of lipid biogenesis. A considerably enriched Golgi fraction from rat brain, together with other submicrosomal fractions, rough and smooth endoplasmic reticulum, plasma membrane, pre-myelin and myelin, will be analyzed for their myelin-specific lipids and for the enzymes (e.g., galactosyl transferase) involved in their synthesis. Preliminary analyses for myelin-specific proteins will also be carried out. Double-label experiments will be employed to follow the progress of assembled lipids through the membranes, from endoplasmic reticulum to myelin, and to assess the possibility of modification of lipid molecules along the way. Attention will be paid to the site of introduction of the extra-long chain, and hydroxy, fatty acids typical for myelin lipids. Efforts will be made to improve the submicrosomal fractionation procedures even further.